Presently, radiation in a band of wavelengths below 300 nm, such as, the bright line or line spectrum of wavelength 253.7 nm, produced for example from a mercury discharge lamp, have come to be used widely in the field of sterilization as well as in the fields of semiconductor manufacture, printing, etc., due to their high photon energies, and the development of radiation sources corresponding to such applications (e.g., the mercury lamp and Excimer laser) has been carried out extensively. As a result, there has been a demand for such techniques designed to accurately measure the energy quantities of single-wavelength radiation in the ultraviolet region, such as, the mercury line spectrum of wavelength 253.7 nm. In addition, there has existed a demand for techniques designed to accurately measure radiation in the wavelength band of below 300 nm, particularly the radiant quantities of wavelengths such as 253.7 nm of the discharge lamp and 184.9 nm of the mercury line spectrum as well as 248 nm of the KrF Excimer laser.
In the past, there has been no Japanese national standard as regards the absolute quantity of the radiation of wavelength 253.7 nm and the measurement of this kind has been effected in the form of measurements by a method in which a filter is combined with a thermal-type detector (usually a thermopile) whose absolute response is calibrated or determined according to the backbody radiation or a luminous intensity standard lamp or spectral irradiance standard lamp calibrated according to the blackbody radiation (Nakagawa et al: "Calibration System of 253.7 nm Irradiance (bactericidal irradiance)", The Illuminating Engineering Institute of Japan, 71-10 (1987) 646).
Then, the thermal-type detector has a low response and also its output variation due to any ambient disturbance is large with resulting deterioration in measuring accuracy. Also, the calibration of the absolute quantity of radiation is effected such that basically the blackbody radiation according to the international temperature scale is used as a primary standard and the value of a total irradiance standard lamp or illuminous intensity standard lamp as a secondary standard is derived from the primary standard thus measuring the absolute quantity of radiation of wavelength 253.7 nm, for example, by using the secondary standard by a method combining a thermal-type detector (e.g., a thermopile) and a filter. Thus, the method is not satisfactory as a practical absolute measurement method in consideration of the accumulation of measuring errors due to the tracing of the value from the primary standard.